Reduction Ratios for Steppers

Hi, ("Joe Newbie" here!)
I'm designing the timing belt reduction that will work the rack &
pinions for my first XYZ table. I know this question has probably
been kicked to death here, but, not even knowing the right search
terms, I'll ask it again:

In designing the drive reduction ratios, how important is it to
achieve a "round" number like [.001" of travel per 1.8 degree motor
step] ?

If the system I settle on comes out to, say, .00125" per step, is it
going to cause me all kinds of setup problems?

And,

Do all [three] axis need to have the exact same drive ratio?

Thanks,
--SC